Low power and Lossy Networks (LLNs), e.g., sensor networks, have a myriad of applications, such as Smart Grid and Smart Cities. Various challenges are presented with LLNs, such as lossy links, low bandwidth, battery operation, low memory and/or processing capability, etc. One example routing solution to LLN challenges is a protocol called Routing Protocol for LLNs or “RPL,” which is a distance vector routing protocol that builds a Destination Oriented Directed Acyclic Graph (DODAG, or simply DAG) in addition to a set of features to bound the control traffic, support local (and slow) repair, etc. The RPL architecture provides a flexible method by which each node performs DODAG discovery, construction, and maintenance.
One of the main challenges in LLNs is not only the limited bandwidth offered by links such as Low Power WiFi, IEEE 802.15.4, or PLC (IEEE P1901.2), but also the very high loss rates experienced on those links and the frequency at which such links may “flap” (be available or not, intermittently). Note that it is not uncommon to lose connectivity for seconds or even minutes, and to see a packet delivery ratio as low as 40% to 50%.
Most existing approaches detect transmission failures using explicit acknowledgments at the Media Access Control (MAC) layer or at higher layers (e.g., transport or application layers). Failure to receive an acknowledgment after attempting a transmission indicates that the intended receiver may not have received the packet. As a result, the transmitter will attempt to retransmit the packet at a later time. In LLNs, dynamic link qualities can easily lead to several retransmissions of a single packet before successfully receiving an acknowledgment. Such an approach can significantly increase communication delay, channel utilization, energy costs associated with transmissions, and other associated transmission costs.